Conventionally, an absolute encoder capable of producing an absolute value signal in a constant time period is constructed as shown in FIG. 4. It should be understood that both the conventional technique and the present invention will be explained by exemplifying vernier type absolute encoders.
FIG. 4 is a block diagram for schematically indicating a signal processing section of the conventional vernier type absolute encoder. In FIG. 4, reference numeral 1 shows a rotary disk; reference numeral 2 indicates a slit stream; reference numeral 3 represents a magnetic sensor; reference numeral 4 denotes a phase modulating section; reference numeral 5 shows a phase difference signal producing section; reference numeral 6 indicates an absolute value signal producing section; reference numeral 7 represents an oscillator; reference numeral 8 denotes a reference signal producing section; reference numeral 9 indicates a modulation signal producing section; reference numeral 20 shows a data transfer section; reference numeral 21 is a motor; and also, reference numeral 22 represents a motor control apparatus.
While positional information of the same equal pitch is formed on the rotary disk 1, 4 sets of the slit streams 2 are provided, the pitch numbers of which are different from each other. The magnetic sensor 3 is constituted by an MR element and a bias magnet, and outputs two phases of sine waves having pitches equal to the slit pitches. The sine wave signals outputted from the magnetic sensor 3 are inputted to the phase modulating section 4 so as to be converted into phase signals φ1, φ2, φ3. The respective phase signals φ1, φ2, φ3 are entered to the phase difference signal producing section 5. The phase difference signal producing section 5 detects phase differences between φ1, φ2, φ3 and φ0 so as to produce phase difference signals (φ0−φ1), (φ0−φ2), (φ0−φ3). These phase difference signals (φ0−φ1), (φ0−φ2), (φ0−φ3) are entered to the absolute value signal producing section 6, so that the absolute signal producing section 6 intermittently, produces an absolute value signal “p” in the time period of the phase signal φ0. Also, since this produced absolute value signal “p” is used so as to control the motor 21 on which the rotary disk 1 is mounted, this absolute value signal “p” is transferred in either a parallel mode or a serial mode by the data transferring section 20 to the motor control apparatus 22 (for instance, republished Japanese Patent No. WO/05553).
However, the conventional technique owns the below-mentioned problems.
FIG. 5 is a diagram for showing a relationship as to motor feedback rotation angles, namely, FIG. 5(a) indicates such a motor feedback rotation angle relationship in the case that a motor control time period and an absolute value producing time period are defined in a synchronous manner, and FIG. 5(b) shows such a motor feedback rotation angle relationship in the case that a motor control time period and an absolute value producing time period are defined in an asynchronous manner.
(1). In the case that the motor 21 which should be controlled is rotated at a constant speed by using the intermittently produced absolute value signal “p”, if the motor control time period of the motor control apparatus 22 is synchronized with the absolute value producing time period, then such a motor feedback rotation angle having no speed variation can be obtained as represented in FIG. 5(a). In order to synchronize the motor control time period with the absolute value producing time period, timing on the side of the motor control apparatus 22 must be matched with timing on the side of the encoder. Also, in such a case that the absolute value producing time period is changed due to changes in technical specifications of the rotary disk 1 and the slit stream 2, technical specifications of the motor control apparatus 22 are also required to be changed.
(2). Also, when the motor control time period is not synchronized with the absolute value producing time period, as represented in FIG. 5(b), the motor feedback rotation angle acquired by the motor control apparatus 22 becomes such a signal having a speed variation, and thus, the encoder can hardly acquire the continuous interpolated absolute value signal.
(3). Also, there is another producing method. That is, an absolute value is read when an initial setting operation is carried out, and thereafter, an incremental signal is produced so as to increment an initial absolute signal. However, in such a case that an erroneous operation occurs due to noise, or the like, there is a problem that errors are stored and an absolute position is shifted.
The present invention has been made to solve the above-described problem, and therefore, has an object to provide both an absolute encoder and an absolute value signal producing process method of the absolute encoder, which are capable of producing a continuous interpolated absolute value signal from an absolute value signal which is intermittently produced in a constant time period, while the interpolated absolute value signal does not depend upon an absolute value producing time period, a control time period of a motor control apparatus, and a transfer method.